Internal combustion engines have historically employed valve train systems that open combustion valves a fixed amount and then return the combustion valve to a closed position. Combustion valves as discussed herein may be either intake valves that allow a charge of air or air and fuel into a combustion chamber of the internal combustion engine or exhaust valves that allow exhaust constituents to be expelled from the combustion chamber of internal combustion engine. More recently, valve train systems have been developed that allow combustion valves to be opened a varying amount in order to achieve desired engine operating characteristics, thereby meeting fuel economy needs, achieving desired engine performance, and reducing emissions. One such valve train system is known as a continuously variable valve lift (CVVL) system in which the magnitude of lift of the combustion valve can be varied to any desired amount between a minimum lift and a maximum lift.
An example of a CVVL system is shown in U.S. Pat. No. 6,988,473 to Rohe et al. In this example, the CVVL system varies the lift of the combustion valve; however, in doing so, the CVVL system also delays the timing during the engine cycle at which the combustion valve begins to open as the lift of the combustion valve is decreased. Delaying the opening of the combustion valve may be acceptable in some systems but may be undesirable in other systems. The arrangement of U.S. Pat. No. 6,988,473 is commonly referred to as a lost motion arrangement because when the CVVL system is controlled to produce less than maximum lift of the combustion valve, a portion of rotation of the mechanism is not transferred to the combustion valve and is used only to compress a lost motion spring.
Another example of a CVVL system is shown in U.S. Pat. No. 5,937,809 to Pierik et al. The CVVL system of U.S. Pat. No. 5,937,809 is also a lost motion arrangement; however, unlike U.S. Pat. No. 6,988,473 discussed above, the CVVL system of U.S. Pat. No. 5,937,809 is arranged to minimize or eliminate the delay in opening of the combustion valve.
What is needed is a valve train system which minimizes or eliminates one or more of the shortcomings as set forth above.